The invention described herein pertains generally to a method and apparatus for drying and sterilizing (pathogen reduction) organic materials, e.g., paper, municipal sewage treatment, grain, and in a second embodiment, depolymerizing polymeric-based materials, e.g., plastics, including crosslinked plastics and rubber-based polymers, including crosslinked rubbers such as sulfur-based crosslinks as used in tires. These organic materials are dried by the direct application of bifurcated out-of-phase microwave energy to the organic materials and convection of combustion products derived from natural gas/liquefied petroleum gas (LPG) through the organic materials, resulting in a reduced moisture content product in one application. A decrosslinked, and at least partially depolymerized product is achieved without convection of combustion products in a second application.
In the field of moisture reduction, escalating costs of natural gas and liquefied petroleum gas are of increasing concern to those involved in the commercial drying of organic materials in paper mills, municipal sewage plants and grain drying plants. With the inherent aging of the facilities, coupled with escalating energy and capital equipment costs, the refurbishing and replacement costs of these plants becomes increasingly difficult to justify. Many efforts to substantially improve throughput efficiency or reduce energy costs have failed to meet their objectives, either from an economic or technical point of view.
In the field of pathogen reduction, there are six alternatives for meeting Class A pathogen requirements pursuant to United States Regulations, 40 CFR, Part 503. These are:
Alternative 1: Thermally Treated Biosolids wherein the biosolids are subjected to one of four time-temperature regimes;
Alternative 2: Biosolids Treated in a High pHxe2x80x94High Temperature process;
Alternative 3: Biosolids Treated in Other Processes wherein it can be demonstrated that reduced enteric values and viable helminth ova values can be achieved;
Alternative 4: Biosolids Treated in Unknown Processesxe2x80x94wherein biosolids can be tested for pathogens salmonella, fecal coliform bacteria, enteric viruses, and viable helminth ova;
Alternative 5: Biosolids Treated in a Process to Further Reduce Pathogens (PFRP); or Alternative 6: Biosolids Treated in a Process Equivalent to a PFRP.
For all of the alternatives listed above, one of two product criteria must be met. Either the density of fecal coliform in the biosolids must be less than 1,000 most probable numbers (MPN) per gram total solids (dry weight basis) or the density of Salmonella bacteria in the biosolids must be less than 3 MPN per 4 grams of total solids (dry weight basis). Either of the above criteria must be met at one of the following times: when the biosolids are used or disposed; when the biosolids are prepared for sale or give-away in a bag or other container for land application; or when the biosolids or derived materials are prepared to meet the requirements for EQ biosolids.
There are four time-temperature regimes for Class A Pathogen Reduction under Alternative 1.
For all of the four time-temperature regimes for Class A Pathogen Reduction, the microwave thermal process exceeds all specifications of Regimes (A-D) for biosolids with 7% solids or greater, which indicates a minimum exposure of 15 seconds or longer at 50xc2x0 C.
In accordance with the present invention in one aspect, there is provided a combined microwave/convection heating, e.g., natural gas, liquefied petroleum gas, ceramic resistance heating, etc., process to more economically produce organic materials suitable for reuse in the agricultural and consumer markets within a specified and controlled moisture content range, as well as reduced pathogens and odor. The invention provides a process for the reduction of moisture content, pathogens and odor from paper mill pulp sludge, sewage treatment plant sludge and grains, the process comprising the direct application of microwave energy to the organic materials with simultaneous convection heating by natural gas/LPG combustion products through the organic materials, resulting in moisture, pathogens, and odor reduction in a predictable, precise, controlled manner.
With biosolids, the process involves the use of microwaves to penetrate the biosolids and in doing so, excite the water molecules, which create heat within milliseconds up to 106xc2x0 C. The microwaves transmitted by each magnetron are rated at a frequency of 915 MHz, with frequencies of this magnitude attacking the single cell pathogens, creating an environment that literally destroys or structurally causes the pathogens to explode. This environment is controlled in the 375 KW microwave thermal chamber/applicator with a variable speed belt for a period of not less than 18 seconds and not more than 30 minutes.
It has been determined that the natural gas/LPG combustion products, which are produced as a direct result from injection into a gas burner and ignited, may also be produced from direct injection of the natural gas/LPG into the combustion chamber of an aero-derivative gas turbine, whose combustion products may be passed through the organic material and subsequently recovered in a combined cycle application for the production of electricity, steam or other waste heat application. The gas turbine is coupled to an electrical generator, which provides electrical power for this invention. It has also been determined that the moisture driven from the products can be: directed into a vapor compressor for the production of high pressure saturated steam and returned to the plant to supplement steam production from an existing boiler; directed into a heat exchanger or condenser for the production of hot water and returned to the plant for plant utility use; directed into a chiller for the production of refrigeration; or directly injected into the combustion chamber of a fired boiler or gas turbine for reduction of carbon monoxide (CO) or nitrogen oxides (NOX). Any or all of these methods of utilization of recovered moisture further contributes to improved economics.
It is an object of this invention to overcome the limitations of the prior art and to provide a means of drying organic materials much more efficiently, sterilize the organic materials, and reduce unpleasant odors, along with reduced energy and capital costs.
It is another object of this invention to provide an improved method for decrosslinking polymers using both microwave and radiant convection energy.
It is still another object of this invention to provide an improved method for depolymerizing polymers using both microwave and radiant convection energy.
It is yet another object of this invention to provide an improved design for the microwave distribution within the chamber.
It is still yet another object of this invention to be portable for demonstration of the above methods to a potential customer at a paper pulp mill, sewage treatment plant or scrap tire facility without additional equipment.
It is additionally an object of this invention to overcome the limitations of the prior art and to provide a means of meeting Class A pathogen requirements.
It is additionally another object of this invention to provide a means of exceeding class A pathogen requirements by a total pathogen kill.